This invention relates to the protection from infection by eucaryotic microorganisms.
Chemically synthesized antimicrobial agents which suppress the growth of eucaryotic microorganisms are well known but many of these agents raise concerns about their safety. It is also known that some antibiotics produced by microorganisms suppress the growth of eucaryotic microorganisms. However, these agents cannot be applied to foods, cosmetics and industrial chemicals due to regulatory controls. Extracts of various spices or garlic have been recognized to have antimicrobial activity but they have peculiar odors, even at low doses, and therefore, their application has been limited.
This invention is directed to safe antimicrobial agents originating from natural sources which are able to suppress the growth of eucaryotic microorganisms and can be applied to foods, cosmetics, pharmaceuticals and industrial chemicals.
As a result of a search for natural sources which are able to suppress the growth of yeasts and molds, it was found that DNA obtained from procaryotic microorganisms suppressed the growth of eucaryotic microorganisms significantly. It is believed that there is a difference in the functional roles between DNA extracted from procaryotic microorganisms and DNA of eucaryotic microorganisms because of differences of methylation and frequency of CG dinucleotide sequences in both microorganisms and that the difference may relate to one of the self-protective functions in procaryotic microorganisms against eucaryotic microorganisms.
The present invention is directed to antimicrobial agents which are effective against eucaryotic microorganisms, in which a major component of the antimicrobial agent is DNA extracted from procaryotic microorganisms and a method of suppressing the growth of eucaryotic microorganisms by the addition of the inventive antimicrobial agent.
In the present invention, the procaryotic micro-organisms include all Gram-positive and Gram-negative bacteria.
The Gram-positive bacteria include those of the Bacillus genus such as B. subtilis, B. cereus., B. megaterium, B. mesentericus, B. licheniformis, B. sphaericus, B. alvei, B. natto and B. circulans; lactic acid bacteria such as Lactobacillus plantarum, L. acidophilus, L. brevis, L. casei, L. delbrueckii, L. fermentum and L. helveticus and Lactococcus lactis, Leuconostoc mesenteroides, L. dextranicum, Pediococcus pentosaceus, P. acidilactici, Streptococcus faecium and Str. faecalis; and Cocci such as Micrococcus luteus, M. flavus, M. roseus, Staphylococcus aureus and S. epidermidis. 
The Gram-negative bacteria include Aeromonas hydrophila, Alcaligenes faecalis, Enterobacter cloacae, K-lebsiella peumoniae, Escherichia coli, Proteus vulgaris, Pseudomonas aeruginosa, Ps. fluorescens, Ps. aureofaciens, Salmonella Typhimurium, Sal. Enteritidis, Serratia marcescens and Vibrio.
When a foodstuff is to be prevented from spoiling or being mixed with a mycotoxin, DNA of a lactic acid bacteria or B. natto, a species of B. substilis used for natto food, or DNA of Escherichia coli can be used in the invention.
DNA of procaryotic microorganisms can be used in the invention to protect materials other than food, plants and living things from eucaryotic microorganisms.
The invention can be used to prevent spoilage of food products and fruit by molds or enzymes produced by the eucaryotes. Eucaryotic microorganisms against which the present invention is effective include those which produce mycotoxins, such as Aflatoxin, Ochratoxin, Sterigmatocystin, Penicillium toxin and Fusarium toxin. Diseases by eumycetes that can be treated by the invention include infections by, for example, trichophyton and candida, plant pathology and fish pathology. Molds on houses, furniture, in the kitchen, bathroom and on floors can be treated by the present invention.
Procaryotic DNA degraded by restriction enzymes also can be used and the size of the DNA is preferably at least 1,000 bases in order to show the growth suppressing effects. It is also favorable for the DNA to contain a large number of CG dinucleotide sequences in the molecule. A CG dinucleotide sequence means that C and G are successive bases in the nucleotide sequence of the procaryotic DNA.
It is preferable that the procaryotic DNA include CG dinucleotide sequences occurring at a frequency of at least two times, more preferably at least 17 times, as in the DNA of the eucaryotic microorganisms.
As eucaryotic microorganisms that are treated by the present invention, yeasts such as Saccharomzyces cerevisiae and Candida albicans and filamentous fungi such as Aspergillus niger and Aspergillus fumigatus are examples.